Simple Defer

gistfile1.js

;(function(){
  
  var slice = [].slice
  
  function push(array, value, length, callback){
    var currentLength = array.push(value)
      , self = this
    if(currentLength === length) self.result = callback.apply(null, array)
  }
  
  function Defer(){
    var args = slice.call(arguments)
      , self = this
      , i = 0
      , length = args.length
      , item
      , stack = self.stack = []
      
    if(!(self instanceof Defer)) return Defer.apply(new Defer, arguments)
    window.setTimeout(function(){
      for(;i < length; i++) { 
        item = args[i]
        push.call(self, stack, typeof item == "function" ? item() : item, length, self.callback)
      }
    }, 0)
    return self
  }
  
  Defer.prototype.then = function(callback){
    var self = this
    self.callback = callback
    return self
  }
  
  window.Defer = Defer
  
})()

new Defer(function(){return "foo"}, 
          function(){return "bar"}, 
          function(){return "baz"})
    .then(function(){console.log(arguments); return arguments})

// this.callback : "then" argument
// this.result : this.callback()
// this.stack : results of "Defer" arguments